Ice making machines, or ice makers, that employ freeze plates which comprise lattice-type cube molds and have gravity water flow and ice harvest are well known and in extensive use. Such machines have received wide acceptance and are particularly desirable for commercial installations such as restaurants, bars, motels and various beverage retailers having a high and continuous demand for fresh ice.
In these ice makers, water is supplied at the top of a freeze plate which directs the water in a tortuous path toward a water pump. A portion of the supplied water collects on the freeze plate, freezes into ice and is identified as sufficiently frozen by suitable means whereupon the freeze plate is defrosted such that the ice is slightly melted and discharged therefrom into a bin. Typically, these ice machines can be classified according to the type of ice they make. One such type is a grid style ice maker which makes generally square ice cubes that form within individual grids of the freeze plate which then form into a continuous sheet of ice cubes as the thickness of the ice increases beyond that of the freeze plate. After harvesting, the sheet of ice cubes will break into individual cubes as they fall into the bin. Another type of ice maker is an individual ice cube maker which makes generally square ice cubes that form within individual grids of the freeze plate which do not form into a continuous sheet of ice cubes. Therefore, upon harvest individual ice cubes fall from the freeze plate and into the bin. Various embodiments of the invention can be adapted to either type of ice maker, and to others not identified, without departing from the scope of the invention. Accordingly, the freeze plate as described herein encompasses any number of types of molds for creating a continuous sheet of ice cubes, individual ice cubes, and/or cubes of different shapes. Control means are provided to control the operation of the ice maker to ensure a constant supply of ice.
It is important to determine when the ice has formed to a sufficient thickness such that it can be harvested. Harvesting too early yields small cubes of ice that may not harvest properly. Harvesting too late yields large chunks of ice that do not easily separate into smaller pieces or individual cubes. Typically, an ice thickness sensor detects the thickness of the ice forming on the freeze plate. When a desired thickness is reached, the sensor signals the ice maker to terminate the freeze cycle and begin a harvest cycle. In the harvest cycle, the refrigeration cycle is reversed and the freeze plate is heated to melt the formed ice cubes away from the freeze plate.
Different devices have been used over the years to determine the ice thickness and thus the appropriate harvest point. Most commercial cube ice machines sold in the United States utilize a hinged sensor located in front of the freeze plate and evaporator to detect the ice thickness in order to initiate harvesting of the ice cubes at the appropriate time. The hinged sensor may use an electrical continuity sensor or an acoustic sensor to directly measure the ice thickness. The hinged sensor approach has the advantage of directly measuring ice thickness as opposed to inferring the thickness from other measurements. This type of system is very common because it is relatively easy to mechanically adjust and provides a relatively accurate ice thickness measurement.
However, this approach has a number of drawbacks. Because the sensor is in the food zone, it must comply with NSF rules for potable water. Thus, the sensor must be made of suitable material and have suitable geometry for use in the food zone of an ice machine, as defined by NSF. Also, the sensor is exposed to the flowing water, so care must be taken to ensure that it will not be adversely affected by the water itself or the scale that may be left on the sensor by the water.
Because the sensor is placed in front of the evaporator assembly and the freeze plate, it must move out of the way when the ice is harvested so that the sensor does not get hit by the falling ice. Thus, the sensor is a moving part which could fail by not moving correctly. The thickness of the ice sensed is a function of how far the sensor is from the ice. Thus the sensor must be in exactly the right position or it will not work as desired. This distance is controlled by a set screw which must be manually adjusted and thus could be adjusted incorrectly or change over time. Additionally, the ice thickness cannot be adjusted electronically because the ice thickness is controlled by the position of the set screw or other mechanical means. Consequently, the ice thickness can only be adjusted mechanically.
In some cases the hinged sensor approach uses electrical conductivity whereby an electrical probe on the sensor is positioned closely adjacent the surface of the evaporator and freeze plate. When ice builds to a desired thickness the electrical probe comes in contact with the flow of water completing an electrical circuit which can trigger the harvest cycle. This method is subject to fouling of the sensor with minerals or other contaminants that would adhere to the sensor and prevent electrical conductivity necessary to signal ice thickness. Additionally, the sensors must be protected from contaminants that would provide an alternate conductivity path. This sensor must also be designed so that the sensor will detect the water even if the water has extremely low conductivity, as is the case with deionized or “DI” water.
U.S. patent application Ser. No. 13/368,814 entitled “System, Apparatus, and Method for Ice Detection” by Rosenlund et al. discloses an acoustic sensor for sensing the thickness of the formed ice. The application proposes an acoustic transmitter that transmits acoustic waves at certain frequencies and an acoustic sensor that senses the reflection of the transmitted waves. When the sensed, reflected waves reach a certain expected amplitude, the system determines that the ice has reached the desired thickness. This sensor is still subject to NSF food zone requirements, still must be moved out of the way during the harvest cycle, and is still subject to placement in the ice maker by mechanical means (e.g., a set screw). Therefore even with an acoustic sensor, the ice thickness can only be adjusted manually, not electronically. Similar to acoustic sensors, capacitive sensors may also be used but suffer from similar drawbacks.
Yet another system for measuring ice thickness is described in U.S. Pat. Nos. 6,405,546 and 6,705,090 each entitled “Ice Maker Control and Harvest Method” granted to Billman et al. The disclosures of each of these patents are incorporated herein by reference. A process disclosed by Billman et al. utilizes a pressure transducer to determine the height of water in the sump of the ice maker and can thus determine when the desired quantity of water is no longer in the sump and instead has been frozen into ice cubes on the freeze plate so that ice harvesting can be started. However, a shortcoming of the Billman et al. patents is that because Billman et al. do not measure ice thickness directly, Billman et al. can mistake water leaks in the system as the formation or non-formation of ice on the freeze plate. For example, if water is leaking from the water system of the ice maker to the environment, Billman et al. will presume the reduced water height is resulting from the formation of ice on the freeze plate rather than water leaking from the system. The systems and methods described by Billman et al. would be fooled by this leak, causing a harvest cycle to occur even though the ice cubes are not fully formed, resulting in undersized ice cubes.
If water is leaking from the water supply into the water system of the ice machine, oversized ice slabs will result because the controller of Billman et al. will incorrectly detect that the higher water level is the result of less freezing, not the result of additional water entering the system. These oversized slabs may be difficult to separate into small pieces of ice or individual cubes. In the case of a serious leakage of water from the water supply into the ice maker water system, the sensor of Billman et al. would continue to make ice long after the desired ice thickness has been reached and a major failure of the ice maker will result, which could include an uncontrolled water leakage into the ice machine's surroundings.
Therefore, there is a need in the art for an ice maker comprising an apparatus and incorporating a method for accurately detecting ice thickness in an ice maker where: the ice thickness sensor is not located in the food zone, the ice thickness sensor is not subjected to the impurities of the water supply, the ice thickness sensor is not a moving part that needs to be moved clear of falling ice during the ice harvest cycle, the ice thickness sensor is not required to be precisely mechanically located and adjusted, and the ice thickness sensor is electronically adjustable. Additionally, there is a need in the art for an ice maker comprising an apparatus and incorporating a method for detecting failure modes of components of the ice maker that can result in damage to the ice maker and the ice maker surroundings.
Four possible failure modes in an ice maker may include: (i) a failure of the water supply to the ice maker; ii) a failure of the ice maker's water inlet valve; iii) a failure of the ice maker's purge valve; and iv) a failure of the ice maker's water pump. For example, a failure of the water supply can be caused by a water supply valve (e.g., a building or facility water supply valve external to the ice machine) being turned off or a failure of the water inlet valve in the ice maker to open. This failure can result in the ice maker running out of water and no longer being able to manufacture ice. A failure of the ice maker's water inlet valve can, if the water inlet valve fails CLOSED, prevent the ice maker from getting water, subsequently preventing the ice maker from making ice. If the water inlet valve fails OPEN, too much water may be supplied to the ice maker, possibly causing a loss in ice making performance (because there is too much water to freeze) or a leak of water into the environment around the ice maker. A failure of the ice maker's purge valve may result in an excess of water impurities collecting in the water in the sump and may cause the ice to be cloudy and/or the ice maker to stop functioning due to mineral accumulation. A failure of the water pump prevents water from being circulated across the freeze plate of the ice maker and thus prevents the making of ice.
Therefore, there is a need in the art for an ice maker comprising an apparatus and incorporating a method for accurately detecting the level of water in the ice maker so that one or more of the following failure modes can be detected: a failure of the water supply, a failure of the water inlet valve, failure of the purge valve, and/or a failure of the water pump.